Computerized ad systems can maintain catalogs of items for multiple merchants. Each catalog item can be one or more computerized records representing, for example, a product the merchant sells. Each catalog item can also be associated with one or more digital images of the product. A merchant may wish to blacklist catalog items that are, for example, illegal or violate the merchant's terms of service. Blacklisting catalog items can prevent those items from being displayed in online advertisements or on the merchant's webpages, in its applications, etc. However, as the size of the catalogs grow, it can be increasingly difficult for an advertiser to detect and identify items that should be blacklisted. As a result, catalog items that should be blacklisted can be inadvertently displayed.